For direct-compression veterinary tablets containing dexamethasone base at unit doses between 0.25 mg and 2.0 mg, content uniformity rather than compactability governs process design. The API is conditioned at 20°C to 25°C and ≤40% relative humidity for at least 4 hours before screening to prevent agglomeration. Micronized material with a particle-size specification of D90 <20 µm is subjected to geometric dilution in 1:10 steps with lactose monohydrate or calcium hydrogen phosphate dihydrate. Each dilution stage is blended in a twin-shell V-blender at 12–15 rpm for 10–15 minutes, and an intensifier bar is operated for 3 minutes after the final addition to break agglomerates. The pre-blend is passed through a conical mill fitted with a 0.8 mm round-hole screen at an impeller speed of 1000–1500 rpm before final blending. Crospovidone or sodium starch glycolate is incorporated extragranularly at 4–6% w/w to maintain disintegration. Magnesium stearate is added last at 0.5–1.0% w/w and mixed for 3–5 minutes, because longer lubrication reduces tablet hardness. Compression on a rotary tablet press with 6 mm flat-faced, scored punches at 5–10 kN produces tablets with hardness 30–60 N and friability not more than 1.0% according to USP <1216>. Content uniformity is assessed from 10 tablets using USP <905>; the acceptance value should remain below 15.0 for the 0.25 mg strength. Disintegration is performed in 900 mL purified water at 37±2°C, with complete disintegration required within 15 minutes. Dissolution testing according to USP <711> uses Apparatus 2 at 50 rpm in 900 mL of 0.1 N hydrochloric acid at 37±0.5°C; the target is not less than 75% released at 45 minutes. Since dexamethasone base is practically insoluble in water, particle-size reduction below 20 µm is the primary release-rate control rather than disintegrant concentration. If the packaging area exceeds 60% relative humidity, the product should be packed in aluminium/aluminium blisters with desiccant, because moisture accelerates hydrolytic degradation of the corticosteroid side chain.

Sterile Filtration Performance Depends on Ionised Dexamethasone Sodium Phosphate Concentration

Aqueous injectable formulations for cattle, horses, swine, dogs, and cats are prepared from dexamethasone sodium phosphate rather than dexamethasone base because the phosphate ester is freely soluble in Water for Injection. The solution is commonly formulated at a concentration equivalent to 2 mg/mL dexamethasone phosphate and buffered with sodium citrate/citric acid to pH 7.0–8.5, consistent with the pharmacopoeial pH range for dexamethasone sodium phosphate injection. For multi-dose vials, benzyl alcohol is incorporated at not more than 1.0% v/v as an antimicrobial preservative; single-dose presentations omit preservative to avoid local tissue reactions. The solution is passed first through a 0.45 µm pre-filter and then through a 0.2 µm PVDF membrane filter. Filter integrity is verified by bubble point or diffusive flow using the membrane manufacturer’s stated threshold, and the filling operation is conducted under ISO Class 5 laminar airflow. Terminal sterilisation at 121°C for 15 minutes may be applied only where stability studies show an increase in related substances of not more than 1.0%. If the product is not terminally sterilised, aseptic processing is validated with media fills per USP <71> and sterile filtration is completed under bioburden control below 10 CFU/100 mL. The finished solution is filled into Type I glass vials with bromobutyl rubber stoppers and nitrogen overlay to reduce headspace oxygen. Storage in amber glass is required because dexamethasone sodium phosphate solutions are light-sensitive. The operational boundary is strict: the solution should not be held longer than 4 hours between sterile filtration and capping unless the hold time is validated, and pH excursions outside 7.0–8.5 accelerate hydrolysis of the phosphate ester.

Manufacture of dexamethasone hard gelatin capsules for feline and canine dose titration starts with the same particle-size-controlled dexamethasone base, but the fill weight is increased to 90–120 mg in a size 3 or size 4 capsule to allow reproducible dosing at 0.25 mg and 0.5 mg. Trituration with lactose monohydrate or microcrystalline cellulose is performed in 1:10 steps, and each blend is passed through a 250 µm sieve before final mixing in a low-shear ribbon mixer at 20–25 rpm for 20 minutes. Magnesium stearate is omitted if dissolution testing shows excessive hydrophobicity; when lubrication is necessary, 0.25% w/w sodium stearyl fumarate is preferred because it has a lower adverse effect on wetting of the hydrophobic active. Encapsulation on an intermittent-motion capsule filler with dosing disc openings of 4–6 mm yields fill-weight relative standard deviation below 2.0% for 20 consecutive capsules. Content uniformity is measured by USP <905> on 10 units; for the 0.25 mg strength, the acceptance value is not more than 15.0. Dissolution is assessed in USP <711> Apparatus 1 at 100 rpm with 900 mL of pH 1.2 simulated gastric fluid; not less than 75% of label claim should dissolve within 45 minutes. Storage at 15–25°C in HDPE bottles with heat-sealed foil induction liners is required because gelatin capsules become brittle below 40% RH and soften above 70% RH. A silica gel desiccant sachet is inserted when the moisture vapour transmission rate of the pack exceeds 0.5 g/m²/day. If the capsule product is intended for use in neonatal calves or pigs, opening the capsule and mixing the contents into milk replacer should be evaluated for dose recovery and light exposure, because dexamethasone in aqueous media degrades more rapidly when unprotected from daylight.

How Does Micronized Dexamethasone Segregation Occur in Oral Powders for Equine Administration?

In sachets containing dexamethasone dispersed in lactose or dextrose, the difference in particle size creates a percolation mechanism during transport vibration. Dexamethasone with D50 5–10 µm and carrier with D50 150–250 µm separate when the filled sachet is vibrated at frequencies typical of road transport, 20–50 Hz, for 60 minutes; fines migrate downward and produce label claim deviations between the first and last sachets. To arrest this, high-shear wet granulation is used to bind dexamethasone onto the carrier. A vertical high-shear granulator with a 10 L bowl is charged with the API-carrier pre-mix and granulated with a binder solution of povidone K30 at 3–5% w/w dissolved in purified water. The impeller runs at 300–500 rpm and the chopper at 1500–2500 rpm for 2–4 minutes. The wet mass is discharged through a 2.0 mm screen and dried in a fluid-bed dryer with inlet air at 60–70°C until loss on drying is not more than 2.5% by Karl Fischer titration. The resulting granules have D50 200–300 µm and a Carr index of 12–18, corresponding to acceptable flow on auger fillers when assessed according to USP <1174>. Sachet fill tolerance is set at ±5% of target weight with in-process checks every 15 minutes. Dispersibility is tested by adding a 5 g sachet to 500 mL water at 25°C and inverting 10 times; no visible aggregate larger than 250 µm should remain after 2 minutes. Packaging consists of aluminium foil laminate because dexamethasone base is photolabile and moisture-sensitive. Storage must remain below 25°C and 60% RH. The processing limit is clear: if granulation moisture exceeds 3.0% w/w, the subsequent drying cycle must be extended and the granules re-screened to avoid cohesive bridging in the auger filler.

When Water-Soluble Granule Premix Meets Groundwater Hardness Above 300 ppm CaCO₃

In poultry or swine drinking-water systems, dexamethasone sodium phosphate is preferred because the ester is freely soluble in water, whereas dexamethasone base is practically insoluble. The granule formulation is designed as a rapidly dispersible water-soluble premix containing anhydrous glucose or sucrose as the main carrier, sodium bicarbonate and citric acid as a pH buffer pair, and povidone or maltodextrin as binder. If groundwater hardness exceeds 300 ppm CaCO₃, the citrate component is increased to reduce insoluble calcium precipitation and maintain dispersion clarity. This is confirmed by adding 10 g of granules to 1 L of hard water at 20°C with paddle stirring at 300 rpm; the solution should become clear within 5 minutes, with residual turbidity below 5 NTU on a nephelometer. Granulation is performed in a top-spray fluid-bed granulator with inlet air at 60–70°C, product temperature 35–40°C, and spray rate 10–15 g/min. Dried granule loss on drying is not more than 1.5%, and purified water used as granulation liquid meets USP <1231> quality criteria. Residual solvents are controlled by VICH GL18, with methanol not more than 3,000 ppm and ethanol not more than 5,000 ppm. The finished granules are packaged in foil-lined pouches. After reconstitution, the medicated water is protected from light and used within 24 hours, because aqueous dexamethasone sodium phosphate undergoes pH-dependent hydrolysis outside the range pH 6.0–8.0. If the receiving water contains oxidising disinfectant residues above 2 ppm free chlorine, the solution should be prepared only after standing or dechlorination to prevent oxidative degradation of the corticosteroid. The operational boundary is critical: do not prepare the medicated water in systems with pH below 5.0 or above 9.0, and do not use water that contains visible iron flocculants, because these conditions reduce active pharmaceutical recovery below the validated dose.

Compounding of dexamethasone into a dermal or otic ointment base requires micronized dexamethasone base, not dexamethasone sodium phosphate, because the phosphate ester has poor partitioning into hydrophobic vehicles. The micronized base is levigated with light mineral oil in a 1:1 slurry using a glass mortar and pestle or an ointment mill. The slurry is then incorporated into white petrolatum previously melted at 45–50°C. High-shear mixing above 60°C is avoided because dexamethasone base degrades under prolonged heating. A three-roll ointment mill with gaps of 50–100 µm on the first pass and 20–30 µm on the second pass is used to disperse agglomerates. The finished ointment is filled into aluminium or epoxy-lined tubes at 25–30°C to prevent phase separation. Assay is performed by HPLC according to USP <621>, with a target content of 95.0–105.0% of the labelled concentration. Microbial quality is tested according to USP <61> and USP <62>; total aerobic microbial count should not exceed 100 CFU/g, and Staphylococcus aureus and Pseudomonas aeruginosa should be absent in 1 g. Otic formulations prepared with polyethylene glycol bases require buffering to pH 5.0–7.0 because dexamethasone phosphate may hydrolyse under strongly acidic or alkaline conditions. If the ointment is intended for otic use, the base should not include lanolin alcohols where the patient has a history of contact sensitisation; white petrolatum and mineral oil alone provide a non-aqueous, water-immiscible matrix that increases residence time. Store the ointment below 30°C and protect from light.

Medicated Premix Carrier Choice and Carryover Limits in Feed Lines

Dry premix for medicated feed lines uses dexamethasone pre-dispersed on vegetable starch or lactose monohydrate carrier. The carrier particle-size range is 100–300 µm with bulk density between 0.45 g/mL and 0.65 g/mL; this range minimises segregation when the premix is metered into a ribbon mixer at an inclusion rate of 0.5–2.0 kg/tonne. The API is added through a geometrically diluted intermediate blend, screened through a 0.5 mm mesh, and mixed for 15–20 minutes in a horizontal ribbon mixer at 60–80 rpm. Homogeneity is confirmed with 10 thief samples collected from defined zones; the relative standard deviation for dexamethasone by HPLC should be below 5.0%. Carryover into the next non-medicated feed batch is measured by HPLC-MS/MS on a flushing batch of ground wheat bran plus fine-ground limestone. A validated flush sequence uses 10 kg bran and 5 kg limestone per 500 kg mixer capacity. The residual dexamethasone level in the flushing batch should be below the limit of quantification; where the product licence establishes the limit, not more than 1 ppm may appear in the first non-medicated feed batch. Because dexamethasone is a potent glucocorticoid, dedicated or validated cleaning procedures are required, and cross-contact with equipment used for prostaglandins or mineral premixes must be assessed by swab recovery studies. Dexamethasone-containing premix is a prescription veterinary medicine; it is not a growth-promotion feed additive, and withdrawal periods set by the national competent authority must be observed for food-producing animals. The feed line should not use alkaline carrier materials with pH above 9.0, because alkaline conditions accelerate chemical degradation of the active during storage at elevated ambient temperatures.